Windows 10 allows users to downgrade their laptop to Windows 8.1 or Windows 7 by clicking the "Go back to Windows 8.1 or 7" button, but this option is only available for a month after upgrading to Windows 10.
The process of cleaning up the Windows.old folder on your computer will take around 1-2 hours, depending on the amount of data stored in it.
When upgrading to Windows 10 from Windows 7 or 8.1, the laptop will create the Windows.old, $Windows.~BT, and $Windows.~WS directories, saving all previous version data in the Windows.old folder. These folders will automatically be deleted after 30 days of running Windows 10, which will then remove the "Go back to Windows 8.1/7" option. However, you can still rollback to the previous version within 30 days by renaming or backing up these folders to another location, keeping their original names.
To revert to Windows 8.1 from Windows 10, change the names of the "Windows.old" and "Windows.~WS" folders to their original names, or restore them to their original location. Then, change your computer's date and time to a date within the 30-day period. This should make the "Go back to Windows 8.
If the upgrade to Windows 10 fails, you can reinstall the previous version of Windows (Windows 8.1 or 7) and then recover your data from the Windows.old folder, which contains a copy of your files and settings from before the upgrade.
To have a simpler and safer way to roll back your laptop to Windows 8.1 or Windows 7, you can create a system backup using the freeware Qiling Disk Master Standard before upgrading to Windows 10. This allows you to easily back up or restore to the previous version of Windows, and even restore your system when your computer fails to boot using the Qiling PXE boot tool or bootable media.
With Qiling Disk Master, you can easily downgrade your laptop from Windows 10 to Windows 8.1 or 7 with just a few clicks, and it also supports dissimilar hardware restore, system clone, file sync, and other useful features.